Here's an irony for you: the Linux kernel is now written, more than ever before, by for-profit corporations, many of which are in direct competition with each other. The total share of contributions by such outfits is rising year over year.

In the latest "Linux Kernel Development" report produced by the Linux foundation, the vast majority of the contributions to kernel development -- more than 80 percent -- are "demonstrably done by developers who are being paid for their work." Translation: The work is being done by programmers contributing to Linux in the service of some corporate paymaster, be it Red Hat, Intel, Suse, Samsung, or Oracle.

The report, now in its fifth edition since 2008, not only tracks who the major contributors are and who they work for, but some of the major trends in the evolution of the kernel. This year's highlights include forward-looking features like the flash-optimized file system F2FS, better automated testing for finding kernel bugs, and growing contributions from the mobile industry.

In fact, it might well be mobile development, rather than server-side, that constitutes the most vital parts of Linux kernel development right now. Texas Instruments and Linaro, two major mobile developers, were the No. 3 and 4 corporate kernel contributors in 2013, respectively. Linaro, a not-for-profit firm co-founded by IBM, Samsung, ARM, and others, was responsible for patches that boosted Android's performance by anywhere from 30 to 100 percent depending on the benchmarks used.

Most of the contributions to the kernel by a given company tend to revolve around what that company wants to get out of Linux, typically to make its own products that much more useful with the operating system. That's obvious for hardware vendors like Intel and Broadcom, and some 9.9 million of the 17 million lines of code in the Linux kernel are for hardware drivers. But in the case of Microsoft -- not as major a contributor as some, but a contributor nonetheless -- it's more about making Linux run that much more efficiently in environments like Azure or Hyper-V.

What's harder to tell is whether or how the growth of corporate contributions to Linux is causing the number of independent contributors to shrink. According to the report, 13.6 percent of the contributions to the kernel do not appear to have any corporate sponsor; around 3.3 percent cannot be reliably traced to one. Those numbers are down from last year.

The Linux Foundation believes it's a matter of indie kernel developers being hired as corporate developers. "[K]ernel developers are in short supply," says the report, "so anybody who demonstrates an ability to get code into the mainline tends not to have trouble finding job offers. Indeed, the bigger problem can be fending those offers off. As a result, volunteer developers tend not to stay that way for long."

One distinction not made in the report is the difference in the amount of contributions made by full-time corporate employees as opposed to paid (or even unpaid) interns. Gnome's Outreach Program for Women, a paid internship program, generated 230-odd changesets that were accepted into Linux in 2013. But it might be impossible to know the full percentage of interns to full-timers without more detailed disclosure on the part of the programmers or their employers,

Another interesting insight revealed by the report, if only indirectly, is which Linux vendors contribute the most back to the kernel. Red Hat and Suse were near the top of the list, with Oracle trailing behind somewhat. But Canonical, creator of Ubuntu, isn't even cited once in the Linux Foundation's report as a significant source of patches. This actually isn't news to those who have followed Canonical for some time, since most of Canonical's contributions to Linux come less in the form of kernel patches and more in the form of marketing and packaging.

Which is more important? Perhaps both are vital to the health of any OS -- as Google, Linux's No. 8 corporate contributor, ought to know well by now.